1. Field of the Invention
The present invention relates to a power generating device which drives a generator by means of a driving device driven by steam.
2. Description of the Prior Art
In order to interconnect a power generating facility to a system, it is necessary to set the frequency of a generated electric power to a commercial frequency (50 Hz or 60 Hz). For this purpose, when the commercial frequency is 60 Hz, the rotational speed of a generator is set to 3600 rpm.
If a turbine which serves as a driving source of a generator is a gas turbine, the drive torque thereof is determined by the quantity of a fuel gas (or air) supplied thereto, and if the turbine is a steam turbine, the drive torque thereof is determined by the quantity of steam supplied thereto. The drive torque and the load torque of the generator then determine the rotational speed of the generator. However, even if the drive torque of the turbine is sufficiently large, since it is necessary to set the rotational speed of the generator to 3600 rpm as described above, adjusting means which adjusts the amount of the fuel gas or the steam is provided upstream of the turbine, and a reduction gear is provided on a drive shaft of the turbine at the same time.
For example, Japanese Patent Laid-Open No. 2000-1705548 discloses a configuration including a fuel flow rate control valve 120 which adjusts the quantity of a supplied fuel and a reduction gear 122 which reduces a turbine rotational speed as shown in FIG. 3. Namely, air compressed by a compressor 124 is supplied as air for combustion to a combustor 126, and the fuel is also supplied to the combustor 126 via the fuel flow rate control valve 120. There is provided such a configuration that a burnt gas from the combustor 126 is fed to a turbine 128, and rotationally drives the turbine 128, and the rotational speed is reduced by the reduction gear 122 provided on a drive shaft of the turbine 128, thereby driving a generator 130.
On the other hand, Japanese Patent Laid-Open No. 2002-84795 discloses such a configuration that, in an electric power generating device which uses a gas turbine engine 140 as a driving source of a generator 142, an electric power at a frequency higher than the commercial frequency is generated, and the electric power at the high frequency is converted into an electric power at the commercial frequency by a power converter 144, as shown in FIG. 4. Namely, in this power generating device, the generator 142 is constituted by a generator which withstands a high rotational speed, the generator 142 is directly coupled to the gas turbine 140, and the gas turbine 140 is driven at a rotational speed of tens to hundreds of thousand rpm to generate an electric power at a high frequency of approximately 1 to 3 kHz. Then, the electric power at the high frequency is once converted into a DC power by a rectifying circuit 146, and is further converted into an AC output in synchronous with the commercial frequency by an inverter 148 for interconnection to the system.
However, the above conventional power generating devices have the following problems. Namely, the configuration, which adjusts the supplied fuel quantity by means of the fuel flow rate control valve in order to restrict the rotational speed of the generator as disclosed in Japanese Patent Laid-Open No. 2000-170548, poses such a problem that the quantity of the fuel gas fed to the turbine is restricted or the steam is discharged wastefully in some cases, resulting in insufficient use of the energy of the fuel gas or the steam. Moreover, since the configuration according to this publication has the reduction gear 122 to reduce the turbine rotational speed, it is impossible to avoid a mechanical loss caused by the reduction gear 122. Moreover, the employment of the reduction gear 122 poses such a problem that a maintenance thereof requires labors.
On the other hand, according to Japanese Patent Laid-Open No. 2002-84795, since the generator 142 can be operated at the high rotational speed, the fuel gas can be sufficiently utilized, and, moreover, since the generator 142 is directly connected to the gas turbine engine 140, this configuration prevents a mechanical loss from being generated therebetween. However, since the gas turbine engine 140 is configured so as to provide the drive at the high speed of tens to hundreds of thousand rpm, and moreover the gas turbine engine 140 is directly connected to the generator 142, there poses a problem of heat generated by the generator 142, resulting in a incapability of a continuous operation at the high rotational speed.